This invention relates to curable fluoropolyether base rubber compositions which are improved in the stability of thermal curing ability over time and suppressed in outgassing and cure into rubbers having improved water repellency, oil repellency, solvent resistance, chemical resistance and weather resistance.
From the past, linear fluoropolyether compounds having at least two alkenyl groups in a molecule and a perfluoroalkyl ether structure in their backbone are used in a wide variety of applications by virtue of advantageous properties of the perfluoroalkyl ether structure. It is known that by blending the curable fluoropolyether compounds with silica fillers commonly used with silicone rubber for reinforcement purposes, mechanical properties of the cured rubber can be drastically improved. Such silica fillers include dry silica also known as fumed silica and wet silica also known as precipitated silica. The blending of silica fillers yields fluoropolyether base rubber compositions having a good profile of heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency, and weather resistance which are satisfactory in most applications.
However, in a particular application where molded rubber parts such as O-rings are used in semiconductor parts, hard disk drives and the like, there is a need for a molding material having minimized outgassing. For such molding material, it is also a problem that a curing behavior changes with time during shelf storage owing to impurities such as amine and sulfur. It is essential for molding material to show a stable curing behavior.
An object of the invention is to provide a curable fluoropolyether base rubber composition which is prevented from changing its curing behavior with time and suppressed in outgassing and cures into rubber having improved properties.
The invention pertains to a curable fluoropolyether base rubber composition comprising (A) a linear fluoropolyether compound having at least two alkenyl groups in a molecule and a perfluoroalkyl ether structure in its backbone, (B) a silica filler having a specific surface area of at least 50 m2/g, (D) an organosilicon compound having at least two hydrogen atoms each attached to a silicon atom in a molecule, and (E) a hydrosilylation catalyst. We have found that the blending of (C) diatomaceous earth in the composition is effective for suppressing the composition""s outgassing and preventing the composition from changing its curing behavior with time under the influence of impurities.
Therefore, the invention provides a curable fluoropolyether base rubber composition comprising the above components (A) to (E).